For the recent years, the vigorous development of the electro-optic industry, particularly the digital camera and the cellular phone camera industries, has placed a larger and larger demand for the optical elements. Of the optical elements, the optical lens can be the most essential and important one.
The optical lens takes many kinds, which are manufactured by different methods depending on the used materials and the applications thereof. For the manufacturing, the production speed of the optical lens has to be promoted with the quality thereof taken into consideration. In this regard, an optical inspection method capable of rapidly and precisely inspecting the optical lens is a long-felt desire in the industry.
Generally, deformity is generally involved in the outline of the lens, e.g. the plastic lens, due to the residual stress or absorbed water therein. Thus, the wavefront of an optical lens is generally presented with the sphere aberration, astigmatism and coma. In the prior art, the inspection of the outline deformation is generally performed by using a profiler. However, the using of the profiler often has the problems of a prolonged inspection time and only some straight line data acquired. Accordingly, the inspection data for determining the quality of the optical lens can not be validly and real time obtained with respect to the mass produced optical lenses.
The polariscope is also utilized to inspect the deformation of the optical lens in the prior art. Due to the crystal structure of the lens, the incident optical beam experiences different indices of refraction when walking through the different crystal directions. This is called the “birefringence” of the crystal. Accordingly, two differently polarized rays are generated when the optical beam goes through the lens, with each of the polarized rays having a vibration direction perpendicular to the other and with one termed as the “ordinary” ray and the other as the “extraordinary” ray. By determining a phase retardation between the ordinary and extraordinary rays, whether the deformation is presented on the lens can be known. However, the birefringence of the lens when not being affected by the residual stress is not significant, it is not possible to detect a sufficient phase retardation variation with respect to the lens by merely using the polariscope.
To overcome the above mentioned problems, the polariscope has to be further improved so that a significant phase retardation variation can be obtained for the inspection of the deformity of the lens. In this regard, the inventors have been involved with a series of intensive research and experiments and finally sets forth an image inspection method by polarized compensation for deformation of lens as the present invention. Compared with the prior art, the present invention is capable of inspecting not only the deformation of the lens by using the real time image but also the residual stress inside the lens. Further, the present invention may be used to inspect the focusing or image quality of an optical system.